1. Field of the Invention
The present invention relates to a process for producing activated carbon for an electrode of an electric double-layer capacitor, and to carbon material for used in such process.
2. Description of the Related Art
To produce such a type of activated carbon, a process is conventionally used, in which a carbon material such as petroleum and coal carbon materials is subjected sequentially to a carbonizing treatment and an alkali activating treatment (for example, see Japanese Patent Application Laid-open No. 2000-77273).
However, since activated carbon for an electrode produced using a carbon material as described above has an electrostatic capacity revealing voltage of as high as 4 V, there is a possibility of the following problems: the expansion amount of two electrodes is increased due to the application of a high voltage, so that a large load is applied to a case of a capacitor, leading to a possibility that the deformation and/or fracture of the case and the short-circuit between the two electrodes, and to a possibility that an electrolyte is decomposed to increase the internal resistance and thus increase the resistance of the capacitor.
Accordingly, it is an object of the present invention to provide a process capable of producing activated carbon for an electrode of a low electrostatic capacity revealing voltage and a high electrostatic capacity density (F/cc) by using a particular carbon material.
To achieve the above object, according to the present invention, there is provided a process for producing activated carbon for an electrode of a electric double-layer capacitor, comprising the steps of: subjecting a carbon material to a carbonizing treatment; and then subjecting the carbon material to an alkali activating treatment; wherein the carbon material used is a condensed polycyclic aromatic compound which has a condensed ring and at least one aliphatic hydrocarbon radical bonded to said condensed ring, said condensed ring including at least one alicyclic hydrocarbon structure moiety; and wherein, in an analysis chart resulting from a 13C-NMR spectroscopy of the condensed polycyclic aromatic compound, a signal intensity ratio IL/IR is equal to or larger than 0.2, and a signal intensity ratio IC/IR is equal to or larger than 0.14, wherein IR represents a signal intensity of an aromatic peak; IL represents a signal intensity of an aliphatic hydrocarbon peak; and IC represents a signal intensity of an alicyclic hydrocarbon peak.
With the above process, it is possible to produce activated carbon for an electrode of a low electrostatic capacity revealing voltage and a high electrostatic capacity density (F/cc). However, if IL/IR less than 0.2 or IC/IR less than 0.14, the electrostatic capacity density (F/cc) is reduced.
According to the present invention, there is provided a carbon material for use in the production of activated carbon for en electrode of an electric double-layer capacitor, which is a condensed polycyclic aromatic compound having a condensed ring and at least one aliphatic hydrocarbon radical R bonded to the condensed ring, the condensed ring including at least one alicyclic hydrocarbon structure moiety, the condensed polycyclic aromatic compound providing, as a result of a 13C-NMR spectroscopy thereof, an analysis chart in which a signal intensity ratio IL/IR is equal to or larger than 0.2, and a signal intensity ratio IC/IR is equal to or larger than 0.14, wherein IR represents a signal intensity of an aromatic peak; IL represents a signal intensity of an aliphatic hydrocarbon peak; and IC represents a signal intensity of an alicyclic hydrocarbon peak.
This carbon material is suitable as a source material for activated carbon for an electrode, as described above.